Thermoplastic crosslinked polyester material and method of molding

ABSTRACT

A POLYANHYDRIDE, SUCHAS A COPOLYMER OF MALEIC ANHYDRIDE AND AN ALPHA-OLEFIN, WHEN HEATED TOGETHER WITH A POLYHYDROXYLATED COMPOUND, SUCH A POLYVINYL ALCOHOL, YIELDS A POLYESTER CROSSLINKED MATERIAL. WHEN HEATED TO A TEMPERATURE IN EXCESS OF 80*C., THIS CROSSLINKED POLYESTER MATERIAL FLOWS AND CAN BE MOLDED. ON SLOW COOLING, THIS MATERIAL MAY AGAIN BECOME CROSSLINKED AND INSOLUBLE IN SOLVENTS SUCH ACETONE.

United States Patent THERMOPLASTIC CROSSLINKED POLYESTER MATERIAL AND METHOD OF MOLDING William J. Heilman, Allison Park, Pa., assignor to Gulf Research 8: Development Company, Pittsburgh, Pa. No Drawing. Filed Aug. 11, 1969, Ser. No. 849,180

Int. Cl. C08f 27/12 US. Cl. 260-785 T 11 Claims ABSTRACT OF THE DISCLOSURE A polyanhydride, such as a copolymer of maleic anhydride and an alpha-olefin, when heated together with a polyhydroxylated compound, such as polyvinyl alcohol, yields a polyester crosslinked material. When heated to a temperature in excess of 80 0., this crosslinked polyester material flows and can be molded. On slow cooling, this material may again become crosslinked and insoluble in solvents such as acetone.

This invention relates to a discovery that certain polyanhydride compounds when reacted with polyhydroxylated compounds will produce a reaction product which possesses the properties of both thermoplastic and thermosetting resins.

The resin art has long sought a resin capable of bridging the gap between the thermosetting and thermoplastic resins. The thermoset resins are typically hard and exhibit a high degree of resistance to chemical solvents. Once crosslinked, however, they become insoluble and infusible, making further manipulation impossible. The thermoplastic resins, on the other hand, are readily fusible but remain soluble and more amenable to chemical attack. A material which combines the most desirable features of both types of resins, that is, a material which is crosslinked so as to be insoluble in chemical solvents and yet which will also flow sufliciently upon heating so as to be remoldable is, to date, a most sought after material.

Indicative of the efforts made previously to obtain a resin which combines the desirable features of both thermosetting and thermoplastic resins is US. Pat. No. 3,272,- 771, dealing with the preparation of the so-called ionomers. The resin described and claimed in the above patent is an ethylene copolymer containing carboxylic acid groups. The copolymer is crosslinked by reacting the acid groups with inorganic compounds. This system is thermoplastic when hot; however, when cool it is crosslinked by an ionic bond to a metal atom, hence the term ionomer. These resins do not have conventional crosslinks of covalent bonds. In addition, the acid salt is subject to ionization by many solvents and chemicals and is neither strong or inert as the covalent bond crosslink.

The invention as described and claimed herein represents a significant advance in the synthesis of compounds which combine both thermoplastic and thermosetting properties. One aspect of this invention is that the resin is crosslinked through covalent bonds which are stronger than the ionic bonds obtained by the prior art, thus approaching more closely the type of bonding found in the thermosetting resins. The resins when cooled demonstrate thermosetting properties, such as insolubility in acetone, yet when heated flow like thermoplastic materials and are capable of being molded in conventional fabricating and molding equipment. These advantages allow the material of the subject invention to avoid the special techniques necessary for the molding and fabricating of thermosetting and elastomeric resins.

In accordance with the invention, a method has been discovered for the preparation of a crosslinked composition of matter which is insoluble in acetone and capable of 3,642,726 Patented Feb. 15, 1972 flowing and being molded at temperatures in excess of C. The method comprises reacting (1) an organic copolymer containing at least one cyclic anhydride group where the carbonyl groups of the cyclic anhydride groups are directly connected to adjacent internal aliphatic carbon atoms and where one of the carbon atoms adjacent said aliphatic carbon atoms contains a substituent larger than hydrogen which is not part of the polymeric chain with (2) a polyhydroxylated compound possessing at least two hydroxide groups directly attached to aliphatic carbon atoms under esterification conditions and wherein the equivalent ratio of the hydroxyl groups in the polyhydroxylated compound to the anhydride groups in the copolymer is from 0.5:1 to 20:1.

In one aspect of this invention a process has been developed which comprises:

heating the solid reaction product of (1) an organic copolymer containing at least one cyclic anhydride group Where the carbonyl groups of the cyclic anhydride groups are directly connected to adjacent internal aliphatic carbon atoms and where one of the carbon atoms adjacent said aliphatic carbon atoms contains a substituent larger than hydrogen which is not part of the polymeric chain and (2) a polyhydroxylated compound possessing at least two hydroxyl groups directly attached to aliphatic carbon atoms and wherein the equivalent ratio of the hydroxyl groups in the polyhydroxylated compound to the anhydride groups in the copolymer is from 0.5 :1 to 20:1 to a temperature above the flow temperature of said solid reaction product and thereafter reforming said solid reaction product by decreasing the temperature to below said flow temperature.

One of the components which is utilized in the method of this invention is an organic copolymer containing at least one cyclic anhydride group where the carbonyl groups of the cyclic anhydride groups are directly connected to adjacent internal aliphatic carbon atoms and where one of the carbon atoms adjacent said aliphatic carbon atom contains a substituent larger than hydrogen which is not a part of the polymeric chain. The organic copolymer, therefore, always has more than four carbon atoms in a straight chain and the carbonyl groups of the anhydride must be directly attached to adjacent internal aliphatic carbon atoms. In addition, one of the carbon atoms adjacent a carbon atom containing the carbonyl function of the anhydride group must contain a substituent, not a part of the polymer chain, which is larger than hydrogen. By internal carbon atoms is meant carbon atoms which do not terminate the carbon chain in the organic compound. The process of this invention is not applicable to aliphatic cyclic anhydrides where the carbonyl groups are on the terminal carbon atoms, such as succinic anhydride; to cyclic anhydrides where the carbonyl groups are directly attached to an aromatic ring, such as phthalic anhydride; or to aliphatic cyclic anhydrides where the carbon atoms adjacent to the cyclic anhydride groups contain only hydrogen substituents, such as ethylene-maleic anhydride c0- polymers.

3 The preferred charge stocks are organic compounds containing at least one divalent radical having the formula:

where R is a hydrocarbon radical having from one to 48 carbon atoms, preferably from four to 18 carbon atoms. By the term hydrocarbon radical in this application is meant any group of atoms consisting of carbon and hydrogen, such as alkyl, cycloalkyl, aryl, alkaryl and aralkyl. Unless otherwise indicated, the term alkyl is meant to include only saturated groups. The term hydrocarbon radical is therefore intended to substantially exclude olefinic unsaturation in the radicals unless otherwise indicated.

The preferred charge stocks are those prepared by the copolymerization of maleic anhydride and an alpha-olefin having from three to 50, preferably six to 20, carbon atoms per molecule.

The maleic anhydride-alpha-olefin copolymers have the formula:

where R is as defined and n is an integer from two to 100. The more preferred charge stocks are those having the formula:

where R" is a hydrocarbon radical having from two to carbon atoms and n is an integer from two to 100, usually from 10 to 50.

The cyclic anhydride containing charge stocks for use in the process of this invention can be prepared in any suitable manner, and their method of preparation or source is not critical. Thus, organic copolymers containing the defined cyclic anhydride groups can be purchased and converted to the desired half-esters in high purity by reaction with an alcohol to be defined below under conditions to be defined below.

The process of the present invention is particularly applicable, however, to the preparation and recovery of halfesters of copolymers of olefinically unsaturated compounds, such as alpha-olefins having at least three carbon atoms with maleic anhydride, which copolymers contain a plurality of internal cyclic anhydride groups. These c0- polymers are generally prepared by methods well known in the art. It is most convenient to perform the polymerization reaction in the presence of a liquid organic diluent which is at least a solvent for the monomers involved in the reaction.

One of the monomers is maleic anhydride, i.e.

It is preferred that the maleic anhydride be substantially free of maleic acid. The maleic anhydride will, of course, react with water to form the undesired maleic acid. Commerical maleic anhydride is suitable for use in the process of this invention, but in the event it is exposed to water and thereby becomes contaminated with maleic acid, means should be employed to remove the maleic acid before the maleic anhydride is used in the subject process. One suitable method of purifying the maleic anhydride is to dissolve the maleic anhydride in a liquid, such as benzene, Which is a solvent for the ma e anhydride but a solvent for the maleic acid. The acid can then be separated by filtration or otherwise and the maleic anhydride recovered by evaporation of the benzene.

The maleic anhydride monomer can be copolymerized with an olefinic compound as represented by the general formula:

where R is as defined above, i.e. a hydrocarbon radical having from one to 48, preferably from four to 18, carbon atoms. The olefinic compound suitably has from three to 50 carbon atoms per molecule, preferably from three to 20, and more preferably from six to ten carbon atoms per molecule.

The preferred olefinic compounds for use in forming the solid polyanhydride are the aliphatic alpha-monoolefins, and in particular, the straight-chain alpha-monoolefins having from three to 20 carbon atoms per molecule.

It is understood that the term olefin is meant to include mixtures of monoolefins having from three to 50 carbon atoms per molecule, such as those obtained by the thermal or catalytic cracking of petroleum stocks. It is desirable that only one olefinic bond per molecule be present in the olefin. Minor amounts of diolcfin, on the order of two percent or less, can, however, be tolerated in the olefin.

Examples of olefin compounds or mixtures of olefins suitable as co-monomers include:

l-tetradecene; tetraisobutylene; Z-octadecene; l-eicosene; Z-methyl-l-nonadeccne;

3-ethyl-2-pentene; 3,3-dimethyl-l-pentene; l-octene; 2-methyl-l-heptene; 3,3-dimethyl-l-hexene;

l-nonene; l-docosene;

4-nonene; l-heptacosene; 4,4-dimethyl-l-heptene; l-hentriacontene; l-decene; 3-heptadecyl-2-eiscosene; Z-decene; Z-methylpenetene-l; l-undecene; Z-methylbutene-l.

The copolymerization can be conducted in any suitable manner. One suitable copolymerization procedure involves contacting the olefinic compound with the maleic anhydride in a suitable solvent in the presence of a freeradical producing catalyst, such as a peroxide. The ratio of the olefinic compound to the maleic anhydride can vary over a wide range, but is generally between about 1:1 and 5:1, with preferred ranges between 1:1 and 3:1. The particularly preferred molar ratios of olefin to anhydride compound will depend to a large extent on the specific olefins employed. For example, for the copolymerization of aliphatic mono-alpha-olefins and maleic anhydride, the ratio of olefin to anhydride is desirably between about 1:1 and 3:1.

The polymerization reaction is a solution-type polymerization wherein the maleic anhydride and olefin monomers are dissolved in a common solvent. The copolymerization can be initiated by any free-radical producing material well known in the art. The preferred free-radical initators are the peroxide-type polymerization initiators and the azo-type polymerization initiators. Benzoyl peroxide is the most preferred initiator. Radiation can also be used to initiate the reaction, if desired.

The peroxide-type free-radical initiator can be organic or inorganic, the organic peroxides having the general formula:

where R, is any organic radical and R is selected from the group consisting of hydrogen and any organic radical. Both R and R can be organic radicals, carrying, if desired, substitutents such as halogens, etc. The most preferred peroxides are the diaroyl and diacyl peroxides.

Examples of suitable peroxides, which in no way are limiting, include benzoyl peroxide; lauroyl peroxide; tertiary butyl peroxide; 2,4-dichlorobenzyl peroxide; tertiary butyl hydroperoxide; cumene hydroperoxide; diacetyl peroxide; actyl hydroperoxide; diethylperoxycarbonate; tertiary butyl perbenzoate; and the various compounds, such as the perborates.

The azo-type compounds, typified by alpha,alpha'-azobis-isobutyronitrile, are also well-known free-radical promoting materials. These azo compounds can be defined as those having present in the molecule group N= N; wherein the valences are satisfied by organic radicals, at least one of which is preferably attached to a tertiary carbon. Other suitable azo compounds include, but are not limited to, p-bromobenzenediazonium fiuoborate; p-tolyldiazoaminobenzene; p-bromobenzene diazonium hydroxide; azomethane and the phenyldiazonium halides. A suitable list of azo-type compounds can be found in US. Pat. 2,551,813, issued May 8, 1951 to Paul Pinkney.

The amount of initiator to employ, exclusive of radiation, of course, depends to a large extent on the particular initiator chosen, the olefin charge stock and the reaction conditions. The initiator must, of course, be soluble in the reaction medium. The usual concentrations of initiator are between 0.001 :1 and 0.1 :1 moles of initiator per mole of maleic anhydride, with preferred amounts between 0.005 :1 and 0.03:1. In general, the more reactive olefins, such as the vinylidene-type, require smaller amounts of the initiator.

The polymerization temperature must be sufficiently high to break down the initiator to produce the desired free-radicals. For example, using benzoyl peroxide as the initiator, the reaction temperature can be between 75 C. and 90 (3., preferably between 80 C. and 85 C. Higher and lower temperatures can be employed, a suitable broad range of temperatures being between 20 C. and 200 C., with preferred temperatures between 50 C. and 120 C.

The reaction pressure should be sufficient to maintain the solvent in the liquid phase. Increased pressure, however, in addition to being an added expense, also promotes unwanted side reactions, such as polymerization of the olefinic compound. Pressures can therefore vary between about atmospheric and 100 p.s.i.g. or higher, but the preferred pressure is atmospheric.

The reaction time is usually sufiicient to result in the substantially complete conversion of the maleic anhydride monomer to copolymer. The reaction time is suitably between one and 24 hours, with preferred reaction times between two and ten hours.

As noted above, the subject reaction is a solution-type polymerization reaction. The olefin, maleic anhydride, solvent and initiator can be brought together in any suitable manner. The important factors are intimate contact of the olefin and maleic anhydride in the presence of a freeradical producing material. The reaction, for example, can be conducted in a batch system Where the olefin is added all initially to a mixture of maleic anhydride, initiator and solvent or the olefin can be added intermittently or continuously to the reaction pot. In another manner, the components in the reaction mixture can be added continuously to a stirred reactor with continuous removal of a portion of the product to a recovery train or to other reactors in series. The reaction can also suitably take place in a coil-type reactor where the components are added at one or more points along the coil.

The reaction solvent, as noted above, must be one which dissolves both the maleic anhydride and the olefinic monomer. It is necessary to dissolve the maleic anhydride and olefinic monomer, so as to bring them into intimate contact in the solution polymerization reaction. It has been found that the solvent must also be one in which the resultant copolymers are soluble, but not so soluble that the copolymers cannot be precipitated out of solution by the addition of a non-solvent for the copolymers.

Suitable solvents include liquid saturated or aromatic hydrocarbons having from six to 20 carbon atoms; ketones having from three to five carbon atoms; the liquid saturated aliphatic dihalogenated hydrocarbons having from one to five carbon atoms per molecule, preferably from one to three carbon atoms per molecule. By liquid is meant liquid under the conditions of polymerization. In the dihalogenated hydrocarbons, the halogens are preferably on adjacent carbon atoms. By halogen is meant F, Cl and Br. The amount of solvent must be such that it can dissolve the maleic anhydride and olefin monomers in addition to the resulting copolymers. The volume ratio of solvent to olefinic monomer is suitably between 1:1 and :1 and is preferably between 1.5 :1 and 4: 1.

The preferred solvents are the saturated hydrocarbons having from six to ten carbon atoms and the saturated dichlorinated hydrocarbons having from one to five, more preferably one to three, carbon atoms.

Examples of suitable solvents include, but are not limited to:

(1) Saturated hydrocarbons such as: hexane; pentane; heptane; octane; and isooctane.

(2) Aromatic hydrocarbons such as: benzene; xylene; and toluene. r

(3) Saturated dihalogenated hydrocarbons such as: dichloromethane; dibromomethane; 1 bromo 2 chloroethane; 1,1-dibromoethane; 1,1-dichloroethane; 1,2-di chloroethane; 1,3-dibromopropane; 1,2-dibromopropane; 1,2-dibromo-2-methylpropane; 1,2-dichloropropane; 1,1- dichloropropane; 1,3-dichloropropane; 1-bromo-2-chloropropane; 1,2-dichlorobutane; 1,5-dibromopentane; and 1,5-dichloropentane.

The molecular weight of the polyanhydride can vary over a wide range. The inherent viscosity (which is a measure of molecular weight) of five grams of the polyanhydride per deciliter of acetone at 77 F. can suitably be between about 0.05 and 1.5 deciliters per gram and is usually from 0.06 to 0.08 deciliters per gram.

Compounds containing the cyclic anhydride groups as defined above are reacted with a non-aromatic polyhydroxylated compound having at least two hydroxyl groups directly attached to aliphatic carbon atoms and preferably containing between ten and 100 hydroxyl groups directly attached to aliphatic carbon atoms. By a nonaromatic polyhydroxylated compound is meant an alcoholic polyhydroxylated compound where the alcoholic hydroxyl groups are not directly attached to an aromatic ring. The aliphatic or alicyclic polyols are preferred. The polyols can be saturated or unsaturated and substituted or unsubstituted. Suitable substituents include halogens. especially chlorine; -OR, where R is a hydrocarbon radical having between one and 20 carbon atoms; nitro; and

where R is hydrogen or CH The group of polyols which are preferred are the saturated unsubstituted polyols containing between two and 200 carbon atoms and between two and 100 hydroxyl groups per molecule. Another group of preferred polyols are the polymeric polyols, such as polyvinylalcohol or cellulose, which are high boiling (usually above 100 C. at 760 mm. Hg) and have a plurality of hydroxyl groups, usually more than two.

Examples of suitable polyols include,but are not limited to, ethylene glycol; propylene glycol; 1,4-butenediol; trimethyl ethane; trimethylol propane; neopentyl glycol; propylene glycols; polyethylene glycols; 1,5-pentanediol; polyvinyl alcohol; cellulose and hexylene glycol (Z-methyl- 2,4-pentanediol). I

It is also possible, and is within the purview of the invention, that a single molecule could have both the polyanhydride and polyol characteristics and be crosslinked through intramolecular esterification. For example, a copolymer of 2-methoxypropylmethacrylate and maleic anhydride containing at least two molecules of each monomer would be satisfactory.

The reaction between the polyanhydride compounds and the polyol is in the nature of an esterification reaction. So long as the proper ratio of the polyhydroxylated compound to the polyanhydride is maintained in the reaction zone the final product, whether prepared thermally or catalytically, will retain the characteristics of flowing at temperatures exceeding the flow temperature of the product, usually above 80 C., even though the hard products at room temperature are insoluble in acetone. The equivalent ratio of hydroxyl groups in the polyhydroxylated compound to anhydride groups in the copolymer is suitably from 0.5:1 to :1 and is preferably from 1:1 to 5:1. However, it is undesirable to achieve total esterification since it is believed to be the breaking of half-ester linkages which renders the product remoldable under the influence of heat and pressure. As a practical matter, the esterification reaction is difficult to promote past the half-ester stage so that total esterification is unlikely even though high ratios of hydroxyl groups to anhydride groups are employed.

The esterification reaction may occur either thermally or catalytically. The advantage of the thermal process is that it is slower and can be followed more closely by, for example, infrared analysis, to insure that a product having the desired percentage of esterification is obtained.

The reaction temperature to promote the esterification reaction between the polyhydroxylated compound and the polyanhydride is suitably between 40 C. and 180 C. The initial reaction temperature can be an elevated temperature of between, for example, 100 C. to 120 C., but at least the final portion of the reaction should be run at a temperature below about 80 C. if it is desirable to react substantially all of the anhydride groups in the polyanhydride since at temperatures exceeding 80 C. an equilibrium exists which prevents at least a portion of the anhydride groups from reacting. It has been found that even though water is not removed from the reaction zone, a greater than 50 percent esterification, for example, to an esterification of 70 percent, can occur.

The reaction pressure is not critical, but should be such that the reactants and products are maintained in the liquid phase. Suitable reaction pressures include atmospheric to 100 p.s.i.g. or higher.

Optionally, a catalyst can be employed to promote the esterification reaction. The catalyst for this reaction can be any material having an ionization constant at C. of at least about 1X l0 Suitable catalysts include liquid mineral acids having the required ionization constants, for example, sulfuric, hydrochloric, nitric and phosphoric acids; organic acids, such as benzene sulfonic and ptoluene sulfonic acids which are readily soluble in the reaction medium; and solid acidic materials including, but not limited to, ion exchange resins. The mineral acids normally come in aqueous solution, and concentrations in aqueous solution between 25 percent and 100 percent are suitable. Concentrations of acid below about 25 percent are especially unsuitable when the higher carbon number (above four) alcohols are employed since the water will form a separate phase in the reactor.

Other suitable acid catalysts include hydrobromic acid; perchloric acid; trichloroacetic acid; iodic acid; and picric acid.

The amount of liquid acid catalyst to employ can vary over a wide range. Usually the weight percent of anhydrous acid based on the weight of copolymer is between 0.05 and five, with preferred anhydrous acid concentrations between 0.1 and one weight percent.

Most of the polyanhydride compounds used as a charge stock to prepare the compositions of this invention are solid under normal conditions. The polyols such as ethylene glycol and propylene glycol are, of course, liquids, but the higher molecular weight polyols are solids. The liquid polyols can be admixed with the solid polyanhydrides and the solid polyanhydrides, if initially insoluble, appear to become soluble in the alcohol as they react to form the crosslinked esterified products. The solid polyols and solid polyanhydrides are suitable intimately admixed on a ball mill or other apparatus so that interaction of the alcoholic hydroxyl groups with the anhydride groups of the polyanhydride is encouraged.

If desired, a mutual solvent can be employed for both of the reactants and solution polymerization can take place. The copolymer gel which is formed can be separated from the reaction solvent by evaporation of the solvent or other suitable procedure.

The reaction time should be sufiicient to result in the formation of the desired percentage of esterification. The usual reaction time is from /2 to 50 hours or more, depending upon whether a thermal or catalytic reaction is employed and on the nature of the reactants. Usual times are from 0.1 to eight hours.

The reaction can be stopped at any suitable place by following the reaction with suitable means such as infrared analysis until the desired amount of anhydride carbonyl absorption peaks disappear. For example, product samples can be removed periodically and subjected to analysis to determine the proportion of carbonyl groups which are still present as anhydride groups. When the desired percentage esterification has occurred, the reaction can be stopped by lowering of reaction temperatures or by other suitable means.

The reaction can be run in a batch or continuous manner.

The reaction products are suitably recovered under conditions such that the temperatures are maintained below about C., preferably between 0 and 60 C. The reaction products are gel-like when in solution and thus are not true solutions.

It has been found that the solid reaction products defined above are usual and unique in their ability at room temperature to be insoluble in organic solvents such as acetone, which is a characteristic of a thermosetting resin, and yet possesses the quality of flowing upon the application of heat. Thus, it is possible to reform the above described solid reaction products with the application of heat in the normal conventional molding processes.

In one aspect of this invention, a process has been discovered which comprises:

heating the solid reaction product of (1) an organic copolymer containing at least one cyclic anhydride group where the carbonyl groups i o) of the cyclic anhydride groups are directly connected to adjacent internal aliphatic carbon atoms and where one of the carbon atoms adjacent said aliphatic carbon atoms contains a substituent larger than hydrogen which is not a part of the polymeric chain and (2) a polyhydroxylated compound possessing at least two hydroxyl groups directly attached to aliphatic carbon atoms and where in the equivalent ratio of the hydroxyl groups in the polyhydroxylated compound to the anhydride groups in the copolymer is from 0.521 to 20: 1; molding said reaction product; and cooling said reaction product to a solid form.

By molding in this application is meant any process which reforms the solid crosslinked product defined above by heating to a temperature in excess of 80 C. Suitable molding procedures may include extrusion, compression molding, injection molding, which terms will be readily understood by those having ordinary skill in this art. As noted, the molding procedure should occur at a temperature in excess of 80 C. to insure that the solid compositions defined above are in a sufficient state of flow so that they may be molded readily. A suitable range of molding temperatures can be from 80 C. to 250 C. but is preferably between 150 C. and 200 C. The state of flow suitable for molding is usually under stress, i.e. pressure to reduce volatility and keep the temperature requirements to a minimum. Thus, molding pressures of atmospheric to 20,000 p.s.i.g. or more are suitable.

While it is not certain, it is believed that when the temperature is increased above the flow temperature of the reaction product, i.e. about 80 C., a suflicient number of half-ester linkages are broken to cause the reaction product to flow, but not so many linkages are broken as to result in any noticeable volatilization, and certainly no removal, of the polyhydroxylated compound. Of course, when the polyhydroxylated compound is selected from the one preferred group of polymeric polyhydroxylated compounds, such as polyvinylalcohol, volatilization is essentially nil. To minimize possible volatilization, the flow temperature should also be minimized. The minimum temperature to produce flow is about 80 C. Preferably, the flow temperature is from about 80 C. to 200 C., although temperatures of up to 250 C. can be employed. Similarly, the time of maintaining the heated reaction products at temperatures above 80 C. should be minimized to aid in preventing or reducing volatilization. Normally the time is very short, on the order of five to 30 minutes, although the time is not a critical factor and can be any suitable time, for example, several hours or more, so long as care is taken by the use of pressure or otherwise to prevent any possible volatilization.

After molding, the product is cooled to be a reformed solid at ambient temperatures. It is preferred to cool the molded product slowly to permit sufficient time and temperature for the half-ester linkages to reform. The rate of cooling is usually from 1 C. to 5 C. per minute. Fast quenching of the molded products is not desirable, especially if the percentage esterification is low or the molding times were long and/or temperatures high.

The invention will be further described with reference to the following experimental work.

EXAMPLE 1 A polyol was prepared by reacting 20 grams of 2-hydroxypropylmethacrylate, 20 grams of styrene and 0.4 gram of benzoyl peroxide in 100 milliliters of benzene. The solution was refluxed at 83 C. for 24 hours. The C0- polymer solution was precipitated by pouring into heptane. The solid copolymer was filtered and dried in a vacuum oven at 50 C. for 20 hours.

The polyanhydride was prepared by reacting 1,470 grams of maleic anhydride, 3,750 milliliters of hexene-l, 36.3 grams of benzoyl peroxide and 750 milliliters of carbon tetrachloride in five liters of ethylene dichloride solvent. The inherent viscosity of the product was 0.093 dl./ g. measured in a solution of five grams of copolymer per 100 milliliters of acetone. The molecular weight of the copolymer was 4,400 as measured by vapor pressure osmometry. The chlorine content was 2.11 percent.

Ten grams of each copolymer were admixed on a ball mill for 24 hours. The mixed copolymers were molded at 350 F. for minutes and slowly cooled at room temperature.

The molded plastic disc was insoluble in acetone at 30 C. indicating that the copolymers were crosslinked. When the molded specimen was heated on a hot plate to about 150 C., unlike the crosslinked thermosetting resin, it melted and flowed. On cooling slowly to room temperature a solid product was again formed.

10 EXAMPLE 2 In the run for this example, 31 grams of ethylene glycol were reacted with 182 grams of the polyhexene-l-maleic anhydride copolymer defined in Example 1 above in the presence of 250 milliliters of methylethylketone and using 0.5 milliliters of pyridine as the catalyst. The solution was heated for 29 hours at 81 C. The gel was placed on a tray in a vacuum oven and the methylethylketone removed at 50 C.

The dried solid was found to be insoluble in acetone. The gel was dried in a vacuum oven at 50 C. for 24 hours. The dried gel was heated to 210 F. where it flowed and was molded under a pressure of about 1000 p.s.i. for 20 minutes. The molded product was slowly cooled to room temperature. A good homogeneous plastic disc was obtained. The molded material was insoluble in acetone but remelted and flowed when heated to about 150 C. on a hot plate.

It should be noted from Example 2 that usually crosslinked polymers cannot be molded.

EXAMPLE 3 It was shown by infrared analysis that ester crosslinks are formed when poly(hexene-l-maleic anhydride) was reacted with ethylene glycol. As crosslinks are formed, the anhydride carbonyl region from 1,923 cm.- to 1,170 cm. disappears and an ester peak forms between 1,770 cm. to 1,667 cmr When the temperature is increased the anhydride peak returns, i.e., when the temperature is increased to above C.

Po1y(hexene-1-maleic anhydride) (20 grams) was heated with ethylene glycol (250 milliliters) at C. for 50 hours. The copolymer produced was found to be insoluble in the glycol but gradually went into solution as a gel. The gel was heated until all of the anhydride groups reacted, as indicated by infrared analysis. The temperature of the gel was increased to 182 C., and at this temperature infrared analysis showed that the anhydride groups are returning and the ester crosslinks are disappearing.

The product of Example 3 above became a flowable material at 182 C. Infrared analysis indicated that not all of the ester crosslinks had been broken but apparently a sufficient number of ester crosslinks had been broken so that the material, which is a solid crosslinked resin at room temperature, is permitted to flow and thus allow the material to be molded and reformed as desired.

The compositions of this invention satisfy a long felt need in the art for a stable material which has a long shelf life at room temperature and which possesses properties at room temperature of crosslinked thermosetting resins yet which will on heating to relatively low temperatures flow and permit itself to 'be reformed and molded by conventional procedures.

Resort may be had to such variations and modifications as fall within the spirit of the invention and the scope of the appended claims.

I claim:

1. A method for the preparation of a crosslinked composition of matter insoluble in acetone and capable of fiowing and being molded at temperatures in excess of 80 C. which comprises reacting (1) an organic copolymer having the formula:

where R is an aliphatic hydrocarbon radical having from 1 to 48 carbon atoms and where in said copolymer the molar ratio of the olefinic portion of the copolymer to the maleic anhydride is about 1:1 with (2) a polyhydroxylated compound possessing at least two hydroxyl groups directly attached to aliphatic carbon atoms under 1 1 esterifieation conditions and wherein the equivalent ratio of the hydroxyl groups in the polyhydroxylated compound to the anhydride groups in the copolymer is from 1:1 to 20:1.

2. A method according to claim 1 wherein the copolymer is the reaction product of maleic anhydride and an alpha-olefin having from 3 to 50 carbon atoms per molecule 3. A method according to claim 2 wherein the polyhydroxylated compound is ethylene glycol.

4. A process according to claim 2 wherein the alphaolefin is l-hexene.

5. A process which comprises:

(1) reacting (a) an organic copolymer having the Where R is an aliphatic hydrocarbon radical having from 1 to 48 car-hon atoms and wherein said copolymer the molar ratio of the olefinic portion of the copolymer to the maleic anhydride is about 1:1 with (b) a polyhydroxylated compound possessing at least two hydroxyl groups directly attached to aliphatic carbon atoms under esterification conditions to form a solid reaction product and wherein the equivalent ratio of the hydroxyl groups in the polyhydroxylated compound to the anhydride groups in the copolymer is from 1:1 to 5:1; and

(2) heating said solid reaction product to a temperature in excess of 80 C. sufiicient to cause said solid reaction product to flow; and

(3) thereafter reforming said solid reaction product by decreasing the temperature to below the flow temperature of said solid reaction product.

6. A process which comprises:

heating the solid reaction product of (1) an aliphatic polyhydroxylated compound containing at least two alcoholic hydroxyl groups directly attached to ali phatic carbon atoms with (2) a copolymer of maleic anhydride and an alpha-olefin having from 3 to carbon atoms per molecule wherein the molar ratio of the alpha-olefin to the maleic anhydride is about 1:1 to a temperature above the flow temperature of said solid reaction product, said temperature being suitable for molding said reaction product;

and wherein said reaction product the equivalent ratio of the alcoholic hydroxyl groups in said polyhydroxylated compound to the anhydride groups in said copolymer is from 1:1 to 20: 1;

molding said reaction products; and

cooling said reaction product to a solid form.

7. A process according to claim 6 wherein the rate of cooling is from 1 C. to 5 C. per minute.

8. A process according to claim 6 wherein the heating is done under condition such that no products are removed.

9. A method according to claim 1 wherein the copolymer is the reaction product of maleic anhydride and an aliphatic alpha-olefin having from 6 to 20 carbon atoms per molecule.

10. A method according to claim 9 wherein the aliphatic alpha-olefin is l-hexene and the polyhydroxylated compound is ethylene glycol.

11. A process according to claim 6 wherein the alphaolefin is an aliphatic alpha-olefin having from 6 to 20 carbon atoms per molecule.

References Cited UNITED STATES PATENTS 3,085,986 4/1963 Muskat 260-31.8 3,299,184 1/1967 Whitworth et al. 260897 3,408,337 10/1968 Moore 260-785 JOSEPH L. SCHOFER, Primary Examiner J. KIGHT III, Assistant Examiner US Cl. X.R. 260-897 B 

